The consensus donor exon:intron junction d(CpApGpGpTpApApGpT) has been synthesized by a modified phosphotriester method. The non-self-complementary nonamer has, in principle, only two G,C or four A,T points of self-recognition. The inference that it exists in the single strand form at 20 degrees C was confirmed by temperature variable 1H-NMR and NOE measurements. The proton assignments were secured using two-dimensional COSY which provided intra-nucleotide correlations, then NOE difference measurements as well as inversion recovery T1 experiments. Systematic procedures were developed for the assignment of the individual bases and their component protons based on the effects of molecular environment on chemical shifts. These latter procedures should be useful for the assignment of other random-coil single strand oligodeoxyribonucleotides.